They can do without the airstone...O2 from the plants should be enough. Don't complicate it too much. I've had a tupperware with no substrate and just some Java fern and moss for the last three years...

Try an 8 or 9 hour schedule for a few weeks with only a 3 hour max mid day spike. If you do begin to win the battle and this algae will eventually turn brown and coverage will get spotty. The ambient...